1
|
Tamtögl A, Chadwick H, Lechner BAJ, Sacchi M. Editorial: Dynamics at surfaces: understanding energy dissipation and physicochemical processes at the atomic and molecular level. Front Chem 2024; 12:1411748. [PMID: 38698938 PMCID: PMC11063948 DOI: 10.3389/fchem.2024.1411748] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2024] [Accepted: 04/10/2024] [Indexed: 05/05/2024] Open
Affiliation(s)
- Anton Tamtögl
- Institute of Experimental Physics, Graz University of Technology, Graz, Austria
| | - Helen Chadwick
- Department of Chemistry, Faculty of Science and Engineering, Swansea University, Swansea, United Kingdom
| | - Barbara A. J. Lechner
- Department of Chemistry, Functional Nanomaterials Group and Catalysis Research Center, School of Natural Sciences, Technical University of Munich, Munich, Germany
| | - Marco Sacchi
- School of Chemistry and Chemical Engineering, University of Surrey, Guildford, United Kingdom
| |
Collapse
|
2
|
Tamtögl A, Sacchi M, Schwab V, Koza MM, Fouquet P. Molecular motion of a nanoscopic moonlander via translations and rotations of triphenylphosphine on graphite. Commun Chem 2024; 7:78. [PMID: 38582953 PMCID: PMC10998885 DOI: 10.1038/s42004-024-01158-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Accepted: 03/22/2024] [Indexed: 04/08/2024] Open
Abstract
Mass transport at surfaces determines the kinetics of processes such as heterogeneous catalysis and thin-film growth, with the diffusivity being controlled by excitation across a translational barrier. Here, we use neutron spectroscopy to follow the nanoscopic motion of triphenylphosphine (P(C6H5)3 or PPh3) adsorbed on exfoliated graphite. Together with force-field molecular dynamics simulations, we show that the motion is similar to that of a molecular motor, i.e. PPh3 rolls over the surface with an almost negligible activation energy for rotations and motion of the phenyl groups and a comparably small activation energy for translation. While rotations and intramolecular motion dominate up to about 300 K, the molecules follow an additional translational jump-motion across the surface from 350-500 K. The unique behaviour of PPh3 is due to its three-point binding with the surface: Along with van der Waals corrected density functional theory calculations, we illustrate that the adsorption energy of PPh3 increases considerably compared to molecules with flat adsorption geometry, yet the effective diffusion barrier for translational motion increases only slightly. We rationalise these results in terms of molecular symmetry, structure and contact angle, illustrating that the molecular degrees of freedom in larger molecules are intimately connected with the diffusivity.
Collapse
Affiliation(s)
- Anton Tamtögl
- Institute of Experimental Physics, Graz University of Technology, Graz, Austria.
| | - Marco Sacchi
- Department of Chemistry, University of Surrey, GU2 7XH, Guildford, UK
| | - Victoria Schwab
- Institute of Experimental Physics, Graz University of Technology, Graz, Austria
| | - Michael M Koza
- Institut Laue-Langevin, 71 Avenue des Martyrs, 38000, Grenoble, France
| | - Peter Fouquet
- Institut Laue-Langevin, 71 Avenue des Martyrs, 38000, Grenoble, France
| |
Collapse
|
3
|
Sabik A, Ellis J, Hedgeland H, Ward DJ, Jardine AP, Allison W, Antczak G, Tamtögl A. Single-molecular diffusivity and long jumps of large organic molecules: CoPc on Ag(100). Front Chem 2024; 12:1355350. [PMID: 38380395 PMCID: PMC10876995 DOI: 10.3389/fchem.2024.1355350] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2023] [Accepted: 01/15/2024] [Indexed: 02/22/2024] Open
Abstract
Energy dissipation and the transfer rate of adsorbed molecules do not only determine the rates of chemical reactions but are also a key factor that often dictates the growth of organic thin films. Here, we present a study of the surface dynamical motion of cobalt phthalocyanine (CoPc) on Ag(100) in reciprocal space based on the helium spin-echo technique in comparison with previous scanning tunnelling microscopy studies. It is found that the activation energy for lateral diffusion changes from 150 meV at 45-50 K to ≈100 meV at 250-350 K, and that the process goes from exclusively single jumps at low temperatures to predominantly long jumps at high temperatures. We thus illustrate that while the general diffusion mechanism remains similar, upon comparing the diffusion process over widely divergent time scales, indeed different jump distributions and a decrease of the effective diffusion barrier are found. Hence a precise molecular-level understanding of dynamical processes and thin film formation requires following the dynamics over the entire temperature scale relevant to the process. Furthermore, we determine the diffusion coefficient and the atomic-scale friction of CoPc and establish that the molecular motion on Ag(100) corresponds to a low friction scenario as a consequence of the additional molecular degrees of freedom.
Collapse
Affiliation(s)
- Agata Sabik
- Institute of Experimental Physics, University of Wrocław, Wrocław, Poland
- Department of Semiconductor Materials Engineering, Wrocław University of Science and Technology, Wrocław, Poland
| | - John Ellis
- Cavendish Laboratory, Cambridge, United Kingdom
| | | | | | | | | | - Grażyna Antczak
- Institute of Experimental Physics, University of Wrocław, Wrocław, Poland
| | - Anton Tamtögl
- Institute of Experimental Physics, Graz University of Technology, Graz, Austria
| |
Collapse
|
4
|
Kyrkjebø S, Cassidy A, Lambrick S, Jardine A, Holst B, Hornekær L. 3He spin-echo scattering indicates hindered diffusion of isolated water molecules on graphene-covered Ir(111). Front Chem 2023; 11:1229546. [PMID: 37867993 PMCID: PMC10587411 DOI: 10.3389/fchem.2023.1229546] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2023] [Accepted: 09/18/2023] [Indexed: 10/24/2023] Open
Abstract
The dynamics of water diffusion on carbon surfaces are of interest in fields as diverse as furthering the use of graphene as an industrial-coating technology and understanding the catalytic role of carbon-based dust grains in the interstellar medium. The early stages of water-ice growth and the mobility of water adsorbates are inherently dependent on the microscopic mechanisms that facilitate water diffusion. Here, we use 3He spin-echo quasi-inelastic scattering to probe the microscopic mechanisms responsible for the diffusion of isolated water molecules on graphene-covered and bare Ir(111). The scattering of He atoms provides a non-invasive and highly surface-sensitive means to measure the rate at which absorbates move around on a substrate at very low coverage. Our results provide an approximate upper limit on the diffusion coefficient for water molecules on GrIr(111) of < 10 - 12 m2/s, an order of magnitude lower than the coefficient that describes the diffusion of water molecules on the bare Ir(111) surface. We attribute the hindered diffusion of water molecules on the GrIr(111) surface to water trapping at specific areas of the corrugated moiré superstructure. Lower mobility of water molecules on a surface is expected to lead to a lower ice nucleation rate and may enhance the macroscopic anti-icing properties of a surface.
Collapse
Affiliation(s)
- Signe Kyrkjebø
- Center for Interstellar Catalysis, Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark
- Interdisciplinary Nanoscience Center, Aarhus University, Aarhus, Denmark
| | - Andrew Cassidy
- Center for Interstellar Catalysis, Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark
| | - Sam Lambrick
- Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom
| | - Andrew Jardine
- Cavendish Laboratory, University of Cambridge, Cambridge, United Kingdom
| | - Bodil Holst
- Institute of Physics and Technology, University of Bergen, Bergen, Norway
| | - Liv Hornekær
- Center for Interstellar Catalysis, Department of Physics and Astronomy, Aarhus University, Aarhus, Denmark
- Interdisciplinary Nanoscience Center, Aarhus University, Aarhus, Denmark
| |
Collapse
|
5
|
Ruckhofer A, Benedek G, Bremholm M, Ernst WE, Tamtögl A. Observation of Dirac Charge-Density Waves in Bi 2Te 2Se. NANOMATERIALS (BASEL, SWITZERLAND) 2023; 13:476. [PMID: 36770437 PMCID: PMC9919891 DOI: 10.3390/nano13030476] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/23/2022] [Revised: 01/18/2023] [Accepted: 01/19/2023] [Indexed: 06/18/2023]
Abstract
While parallel segments in the Fermi level contours, often found at the surfaces of topological insulators (TIs), would imply "strong" nesting conditions, the existence of charge-density waves (CDWs)-periodic modulations of the electron density-has not been verified up to now. Here, we report the observation of a CDW at the surface of the TI Bi2Te2Se(111), below ≈350K, by helium-atom scattering and, thus, experimental evidence for a CDW involving Dirac topological electrons. Deviations of the order parameter observed below 180K, and a low-temperature break of time reversal symmetry, suggest the onset of a spin-density wave with the same period as the CDW in the presence of a prominent electron-phonon interaction, originating from Rashba spin-orbit coupling.
Collapse
Affiliation(s)
- Adrian Ruckhofer
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria
| | - Giorgio Benedek
- Dipartimento di Scienza dei Materiali, Università degli Studi di Milano-Bicocca, Via R. Cozzi 55, 20125 Milano, Italy
- Donostia International Physics Center, University of the Basque Country, Paseo M. de Lardizabal 4, 20018 Donostia/San Sebastián, Spain
| | - Martin Bremholm
- Centre for Materials Crystallography, Department of Chemistry and iNANO, Aarhus University, 8000 Aarhus, Denmark
| | - Wolfgang E. Ernst
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria
| | - Anton Tamtögl
- Institute of Experimental Physics, Graz University of Technology, Petersgasse 16, 8010 Graz, Austria
| |
Collapse
|
6
|
Maier P, Xavier NF, Truscott CL, Hansen T, Fouquet P, Sacchi M, Tamtögl A. How does tuning the van der Waals bonding strength affect adsorbate structure? Phys Chem Chem Phys 2022; 24:29371-29380. [PMID: 36448738 DOI: 10.1039/d2cp03468a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Organic molecular thin-films are employed for manufacturing a wide variety of electronic devices, including memory devices and transistors. A precise description of the atomic-scale interactions in aromatic carbon systems is of paramount importance for the design of organic thin-films and carbon-based nanomaterials. Here we investigate the binding and structure of pyrazine on graphite with neutron diffraction and spin-echo measurements. Diffraction data of the ordered phase of deuterated pyrazine, (C4D4N2), adsorbed on the graphite (0001) basal plane surface are compared to scattering simulations and complemented by van der Waals corrected density functional theory calculations. The lattice constant of pyrazine on graphite is found to be (6.06 ± 0.02) Å. Compared to benzene (C6D6) adsorption on graphite, the pyrazine overlayer appears to be much more thermodynamically stable, up to 320 K, and continues in layer-by-layer growth. Both findings suggest a direct correlation between the intensity of van der Waals bonding and the stability of the self-assembled overlayer because the nitrogen atoms in the six-membered ring of pyrazine increase the van der Waals bonding in comparison to benzene, which only contains carbon atoms.
Collapse
Affiliation(s)
- Philipp Maier
- Institute of Experimental Physics, Graz University of Technology, 8010 Graz, Austria.
| | - Neubi F Xavier
- Department of Chemistry, University of Surrey, Guildford GU2 7XH, UK
| | - Chris L Truscott
- Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, UK
| | - Thomas Hansen
- Institut Laue-Langevin, 71 Avenue des Martyrs, 38000 Grenoble, France
| | - Peter Fouquet
- Institut Laue-Langevin, 71 Avenue des Martyrs, 38000 Grenoble, France
| | - Marco Sacchi
- Department of Chemistry, University of Surrey, Guildford GU2 7XH, UK
| | - Anton Tamtögl
- Institute of Experimental Physics, Graz University of Technology, 8010 Graz, Austria.
| |
Collapse
|
7
|
Sacchi M, Tamtögl A. Water adsorption and dynamics on graphene and other 2D materials: Computational and experimental advances. ADVANCES IN PHYSICS: X 2022; 8:2134051. [PMID: 36816858 PMCID: PMC7614201 DOI: 10.1080/23746149.2022.2134051] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Revised: 09/26/2022] [Accepted: 09/27/2022] [Indexed: 06/18/2023] Open
Abstract
The interaction of water and surfaces, at molecular level, is of critical importance for understanding processes such as corrosion, friction, catalysis and mass transport. The significant literature on interactions with single crystal metal surfaces should not obscure unknowns in the unique behaviour of ice and the complex relationships between adsorption, diffusion and long-range inter-molecular interactions. Even less is known about the atomic-scale behaviour of water on novel, non-metallic interfaces, in particular on graphene and other 2D materials. In this manuscript, we review recent progress in the characterisation of water adsorption on 2D materials, with a focus on the nano-material graphene and graphitic nanostructures; materials which are of paramount importance for separation technologies, electrochemistry and catalysis, to name a few. The adsorption of water on graphene has also become one of the benchmark systems for modern computational methods, in particular dispersion-corrected density functional theory (DFT). We then review recent experimental and theoretical advances in studying the single-molecular motion of water at surfaces, with a special emphasis on scattering approaches as they allow an unparalleled window of observation to water surface motion, including diffusion, vibration and self-assembly.
Collapse
Affiliation(s)
- M. Sacchi
- Department of Chemistry, University of Surrey, Guildford GU2 7XH, UK
| | - A. Tamtögl
- Institute of Experimental Physics, Graz University of Technology, 8010 Graz, Austria
| |
Collapse
|
8
|
Ruckhofer A, Sacchi M, Payne A, Jardine AP, Ernst WE, Avidor N, Tamtögl A. Evolution of ordered nanoporous phases during h-BN growth: controlling the route from gas-phase precursor to 2D material by in situ monitoring. NANOSCALE HORIZONS 2022; 7:1388-1396. [PMID: 36205333 PMCID: PMC9590587 DOI: 10.1039/d2nh00353h] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/28/2022] [Accepted: 09/20/2022] [Indexed: 06/16/2023]
Abstract
Large-area single-crystal monolayers of two-dimensional (2D) materials such as graphene and hexagonal boron nitride (h-BN) can be grown by chemical vapour deposition (CVD). However, the high temperatures and fast timescales at which the conversion from a gas-phase precursor to the 2D material appears, make it extremely challenging to simultaneously follow the atomic arrangements. We utilise helium atom scattering to discover and control the growth of novel 2D h-BN nanoporous phases during the CVD process. We find that prior to the formation of h-BN from the gas-phase precursor, a metastable (3 × 3) structure is formed, and that excess deposition on the resulting 2D h-BN leads to the emergence of a (3 × 4) structure. We illustrate that these nanoporous structures are produced by partial dehydrogenation and polymerisation of the borazine precursor upon adsorption. These steps are largely unexplored during the synthesis of 2D materials and we unveil the rich phases during CVD growth. Our results provide significant foundations for 2D materials engineering in CVD, by adjusting or carefully controlling the growth conditions and thus exploiting these intermediate structures for the synthesis of covalent self-assembled 2D networks.
Collapse
Affiliation(s)
- Adrian Ruckhofer
- Institute of Experimental Physics, Graz University of Technology, Graz, Austria.
| | - Marco Sacchi
- Department of Chemistry, University of Surrey, Guildford GU2 7XH, UK
| | - Anthony Payne
- Department of Chemistry, University of Surrey, Guildford GU2 7XH, UK
| | - Andrew P Jardine
- Cavendish Laboratory, J. J. Thompson Avenue, Cambridge CB3 0HE, UK.
| | - Wolfgang E Ernst
- Institute of Experimental Physics, Graz University of Technology, Graz, Austria.
| | - Nadav Avidor
- Cavendish Laboratory, J. J. Thompson Avenue, Cambridge CB3 0HE, UK.
| | - Anton Tamtögl
- Institute of Experimental Physics, Graz University of Technology, Graz, Austria.
| |
Collapse
|
9
|
Schmutzler SJ, Ruckhofer A, Ernst WE, Tamtögl A. Surface electronic corrugation of a one-dimensional topological metal: Bi(114). Phys Chem Chem Phys 2022; 24:9146-9155. [PMID: 35191440 PMCID: PMC9020329 DOI: 10.1039/d1cp05284e] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2021] [Accepted: 02/09/2022] [Indexed: 12/03/2022]
Abstract
The surface of Bi(114) is a striking example where the reduced dimensionality gives rise to structural rearrangement and new states at the surface. Here, we present a study of the surface structure and electronic corrugation of this quasi one-dimensional topological metal based on helium atom scattering (HAS) measurements. In contrast to low-index metal surfaces, upon scattering from the stepped (114) truncation of Bi, a large proportion of the incident beam is scattered into higher order diffraction channels which in combination with the large surface unit cell makes an analysis challenging. The surface electronic corrugation of Bi(114) is determined, using measurements upon scattering normal to the steps, together with quantum mechanical scattering calculations. Therefore, minimisation routines that vary the shape of the corrugation are employed, in order to minimise the deviation between the calculations and experimental scans. Furthermore, we illustrate that quantum mechanical scattering calculations can be used to determine the orientation of the in- and outgoing beam with respect to the stepped surface structure.
Collapse
Affiliation(s)
- Stephan J Schmutzler
- Institute of Experimental Physics, Graz University of Technology, 8010 Graz, Austria.
- Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin, Germany
| | - Adrian Ruckhofer
- Institute of Experimental Physics, Graz University of Technology, 8010 Graz, Austria.
| | - Wolfgang E Ernst
- Institute of Experimental Physics, Graz University of Technology, 8010 Graz, Austria.
| | - Anton Tamtögl
- Institute of Experimental Physics, Graz University of Technology, 8010 Graz, Austria.
| |
Collapse
|
10
|
Tamtögl A, Bahn E, Sacchi M, Zhu J, Ward DJ, Jardine AP, Jenkins SJ, Fouquet P, Ellis J, Allison W. Motion of water monomers reveals a kinetic barrier to ice nucleation on graphene. Nat Commun 2021; 12:3120. [PMID: 34035257 PMCID: PMC8149658 DOI: 10.1038/s41467-021-23226-5] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Accepted: 04/16/2021] [Indexed: 02/04/2023] Open
Abstract
The interfacial behaviour of water remains a central question to fields as diverse as protein folding, friction and ice formation. While the properties of water at interfaces differ from those in the bulk, major gaps in our knowledge limit our understanding at the molecular level. Information concerning the microscopic motion of water comes mostly from computation and, on an atomic scale, is largely unexplored by experiment. Here, we provide a detailed insight into the behaviour of water monomers on a graphene surface. The motion displays remarkably strong signatures of cooperative behaviour due to repulsive forces between the monomers, enhancing the monomer lifetime ( ≈ 3 s at 125 K) in a free-gas phase that precedes the nucleation of ice islands and, in turn, provides the opportunity for our experiments to be performed. Our results give a molecular perspective on a kinetic barrier to ice nucleation, providing routes to understand and control the processes involved in ice formation.
Collapse
Affiliation(s)
- Anton Tamtögl
- Cavendish Laboratory, University of Cambridge, Cambridge, UK.
- Institute of Experimental Physics, Graz University of Technology, Graz, Austria.
| | - Emanuel Bahn
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
- Department of Radiation Oncology, Heidelberg University Hospital, Heidelberg, Germany
| | - Marco Sacchi
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK.
- Department of Chemistry, University of Surrey, Guildford, UK.
| | - Jianding Zhu
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - David J Ward
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | | | - Stephen J Jenkins
- Yusuf Hamied Department of Chemistry, University of Cambridge, Cambridge, UK
| | | | - John Ellis
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - William Allison
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| |
Collapse
|
11
|
Kelsall J, Townsend PSM, Ellis J, Jardine AP, Avidor N. Ultrafast Diffusion at the Onset of Growth: O/Ru(0001). PHYSICAL REVIEW LETTERS 2021; 126:155901. [PMID: 33929255 DOI: 10.1103/physrevlett.126.155901] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/08/2020] [Accepted: 03/05/2021] [Indexed: 06/12/2023]
Abstract
Nanoscopic clustering in a 2D disordered phase is observed for oxygen on Ru(0001) at low coverages and high temperatures. We study the coexistence of quasistatic clusters (with a characteristic length of ∼9 Å) and highly mobile atomic oxygen which diffuses between the energy-inequivalent, threefold hollow sites of the substrate. We determine a surprisingly low activation energy for diffusion of 385±20 meV. The minimum of the O-O interadsorbate potential appears to be at lower separations than previously reported.
Collapse
Affiliation(s)
- Jack Kelsall
- Cavendish Laboratory, University of Cambridge, 19 J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Peter S M Townsend
- Department of Chemistry and Chemical Biology, Rutgers University, Piscataway, New Jersey 08854, USA
| | - John Ellis
- Cavendish Laboratory, University of Cambridge, 19 J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Andrew P Jardine
- Cavendish Laboratory, University of Cambridge, 19 J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| | - Nadav Avidor
- Cavendish Laboratory, University of Cambridge, 19 J J Thomson Avenue, Cambridge CB3 0HE, United Kingdom
| |
Collapse
|
12
|
Raghavan A, Slocombe L, Spreinat A, Ward DJ, Allison W, Ellis J, Jardine AP, Sacchi M, Avidor N. Alkali metal adsorption on metal surfaces: new insights from new tools. Phys Chem Chem Phys 2021; 23:7822-7829. [PMID: 33179674 DOI: 10.1039/d0cp05365a] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The adsorption of sodium on Ru(0001) is studied using 3He spin-echo spectroscopy (HeSE), molecular dynamics simulations (MD) and density functional theory (DFT). In the multi-layer regime, an analysis of helium reflectivity, gives an electron-phonon coupling constant of λ = 0.64 ± 0.06. At sub-monolayer coverage, DFT calculations show that the preferred adsorption site changes from hollow site to top site as the supercell increases and the effective coverage, θ, is reduced from 0.25 to 0.0625 adsorbates per substrate atom. Energy barriers and adsorption geometries taken from DFT are used in molecular dynamics calculations to generate simulated data sets for comparison with measurements. We introduce a new Bayesian method of analysis that compares measurement and model directly, without assuming analytic lineshapes. The value of adsorbate-substrate energy exchange rate (friction) in the MD simulation is the sole variable parameter. Experimental data at a coverage θ = 0.028 compares well with the low-coverage DFT result, giving an effective activation barrier Eeff = 46 ± 4 meV with a friction γ = 0.3 ps-1. Better fits to the data can be achieved by including additional variable parameters, but in all cases, the mechanism of diffusion is predominantly on a Bravais lattice, suggesting a single adsorption site in the unit cell, despite the close packed geometry.
Collapse
Affiliation(s)
- Arjun Raghavan
- Cavendish Laboratory, University of Cambridge, Cambridge CB30HE, UK.
| | | | | | | | | | | | | | | | | |
Collapse
|
13
|
Tamtögl A, Ruckhofer A, Campi D, Allison W, Ernst WE. Atom-surface van der Waals potentials of topological insulators and semimetals from scattering measurements. Phys Chem Chem Phys 2021; 23:7637-7652. [PMID: 33492313 DOI: 10.1039/d0cp05388k] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The phenomenology of resonant scattering has been known since the earliest experiments upon scattering of atomic beams from surfaces and is a means of obtaining experimental information about the fundamentals of weak adsorption systems in the van der Waals regime. We provide an overview of the experimental approach based on new experimental data for the He-Sb2Te3(111) system, followed by a comparative overview and perspective of recent results for topological semimetal and insulator surfaces. Moreover, we shortly discuss the perspectives of calculating helium-surface interaction potentials from ab initio calculations. Our perspective demonstrates that atom-surface scattering provides direct experimental information about the atom-surface interaction in the weak physisorption regime and can also be used to determine the lifetime and mean free path of the trapped atom. We further discuss the effects of elastic and inelastic scattering on the linewidth and lifetime of the trapped He atom with an outlook on future developments and applications.
Collapse
Affiliation(s)
- Anton Tamtögl
- Institute of Experimental Physics, Graz University of Technology, 8010 Graz, Austria.
| | | | | | | | | |
Collapse
|
14
|
Ward DJ, Raghavan A, Tamtögl A, Jardine AP, Bahn E, Ellis J, Miret-Artès S, Allison W. Inter-adsorbate forces and coherent scattering in helium spin-echo experiments. Phys Chem Chem Phys 2021; 23:7799-7805. [PMID: 33331836 DOI: 10.1039/d0cp04539j] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
In studies of dynamical systems, helium atoms scatter coherently from an ensemble of adsorbates as they diffuse on the surface. The results give information on the co-operative behaviour of interacting adsorbates and thus include the effects of both adsorbate-substrate and adsorbate-adsorbate interactions. Here, we discuss a method to disentangle the effects of interactions between adsorbates from those with the substrate. The result gives an approximation to observations that would be obtained if the scattering was incoherent. Information from the experiment can therefore be used to distinguish more clearly between long-range inter-adsorbate forces and the short range effects arising from the local lattice potential and associated thermal excitations. The method is discussed in the context of a system with strong inter-adsorbate interactions, sodium atoms diffusing on a copper (111) surface.
Collapse
Affiliation(s)
- David J Ward
- Cavendish Laboratory, J.J. Thomson Ave., Cambridge, CB3 0HE, UK.
| | | | | | | | | | | | | | | |
Collapse
|
15
|
Holst B, Alexandrowicz G, Avidor N, Benedek G, Bracco G, Ernst WE, Farías D, Jardine AP, Lefmann K, Manson JR, Marquardt R, Artés SM, Sibener SJ, Wells JW, Tamtögl A, Allison W. Material properties particularly suited to be measured with helium scattering: selected examples from 2D materials, van der Waals heterostructures, glassy materials, catalytic substrates, topological insulators and superconducting radio frequency materials. Phys Chem Chem Phys 2021; 23:7653-7672. [PMID: 33625410 DOI: 10.1039/d0cp05833e] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Helium Atom Scattering (HAS) and Helium Spin-Echo scattering (HeSE), together helium scattering, are well established, but non-commercial surface science techniques. They are characterised by the beam inertness and very low beam energy (<0.1 eV) which allows essentially all materials and adsorbates, including fragile and/or insulating materials and light adsorbates such as hydrogen to be investigated on the atomic scale. At present there only exist an estimated less than 15 helium and helium spin-echo scattering instruments in total, spread across the world. This means that up till now the techniques have not been readily available for a broad scientific community. Efforts are ongoing to change this by establishing a central helium scattering facility, possibly in connection with a neutron or synchrotron facility. In this context it is important to clarify what information can be obtained from helium scattering that cannot be obtained with other surface science techniques. Here we present a non-exclusive overview of a range of material properties particularly suited to be measured with helium scattering: (i) high precision, direct measurements of bending rigidity and substrate coupling strength of a range of 2D materials and van der Waals heterostructures as a function of temperature, (ii) direct measurements of the electron-phonon coupling constant λ exclusively in the low energy range (<0.1 eV, tuneable) for 2D materials and van der Waals heterostructures (iii) direct measurements of the surface boson peak in glassy materials, (iv) aspects of polymer chain surface dynamics under nano-confinement (v) certain aspects of nanoscale surface topography, (vi) central properties of surface dynamics and surface diffusion of adsorbates (HeSE) and (vii) two specific science case examples - topological insulators and superconducting radio frequency materials, illustrating how combined HAS and HeSE are necessary to understand the properties of quantum materials. The paper finishes with (viii) examples of molecular surface scattering experiments and other atom surface scattering experiments which can be performed using HAS and HeSE instruments.
Collapse
Affiliation(s)
- Bodil Holst
- Department of Physics and Technology, University of Bergen, Allegaten 55, 5007 Bergen, Norway.
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | |
Collapse
|
16
|
Civita D, Kolmer M, Simpson GJ, Li AP, Hecht S, Grill L. Control of long-distance motion of single molecules on a surface. Science 2020; 370:957-960. [PMID: 33214276 DOI: 10.1126/science.abd0696] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Accepted: 08/27/2020] [Indexed: 11/02/2022]
Abstract
Spatial control over molecular movement is typically limited because motion at the atomic scale follows stochastic processes. We used scanning tunneling microscopy to bring single molecules into a stable orientation of high translational mobility where they moved along precisely defined tracks. Single dibromoterfluorene molecules moved over large distances of 150 nanometers with extremely high spatial precision of 0.1 angstrom across a silver (111) surface. The electrostatic nature of the effect enabled the selective application of repulsive and attractive forces to send or receive single molecules. The high control allows us to precisely move an individual and specific molecular entity between two separate probes, opening avenues for velocity measurements and thus energy dissipation studies of single molecules in real time during diffusion and collision.
Collapse
Affiliation(s)
- Donato Civita
- Department of Physical Chemistry, University of Graz, Heinrichstrasse 28, 8010 Graz, Austria
| | - Marek Kolmer
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Grant J Simpson
- Department of Physical Chemistry, University of Graz, Heinrichstrasse 28, 8010 Graz, Austria
| | - An-Ping Li
- Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA
| | - Stefan Hecht
- Department of Chemistry and IRIS Adlershof, Humboldt-Universität zu Berlin, Brook-Taylor-Str. 2, 12489 Berlin, Germany.,DWI -Leibniz Institute for Interactive Materials, Forckenbeckstr. 50, 52074 Aachen, Germany.,Institute of Technical and Macromolecular Chemistry, RWTH Aachen University, Worringer Weg 2, 52074 Aachen, Germany
| | - Leonhard Grill
- Department of Physical Chemistry, University of Graz, Heinrichstrasse 28, 8010 Graz, Austria.
| |
Collapse
|